It is required to reduce the power consumption for an LSI (Large Scale Integration) used for a mobile device, and it is required to improve the performance for an LSI used for a mobile device.
Then, realizing the optimization and low power consumption supplied to an LSI circuit by arranging a plurality of power supply systems in an LSI circuit in which potentials of the power supply systems can be independently set, and by controlling potentials of the power supply systems in accordance with the operation situation of the LSI circuit.
Further, the above-mentioned optimization is performed by DC/DC converters corresponding to the power supply systems in the LSI for supplying power to the LSI and a controller for controlling the plurality of the DC/DC converter.
Herein, in the optimization in accordance with the operation situation of the LSI, such operations are properly executed that power is supplied only to an operation circuit, a low voltage is applied to a circuit to which a low operation-frequency is required, and a rated voltage is supplied to a circuit to which processing is performed with high load.
However, if a plurality of power supply systems exists in the LSI circuit and voltages of the power supply systems are controlled as mentioned above, a mechanism for suppressing the voltage change is required for the power supply systems. Because by reducing parasitic capacitance connected to the power supply systems, by dividing the power supply systems, the voltage of the power supply systems are easily affected by the voltage change from another power supply system. Further, if the parasitic capacitance connected to the power supply systems becomes low level, it takes a long time to stabilize the voltage upon raising the voltage in the power supply system for processing with high load.
Then, it is proposed that a capacitance cell that is sufficient to stabilize the voltage, i.e., suppress the power noise is calculated and is inserted between a high-voltage power supply and a low-voltage power supply in the power supply systems (e.g., refer to Technical information magazine “FIND” Vol. 22 No. 5 in 2004 for user of Fujitsu Limited (pages 47 to 51)).
According to Technical information magazine “FIND” Vol. 22 No. 5 in 2004 for user of Fujitsu Limited, it is proposed that, in consideration of operations and signal delay of components in the devices in the LSI due to the power noise, the amount of capacitance cells best to suppress the power noise is calculated and is inserted in the LSI. Then, it is possible to ensure the compensation capacitance to suppress the voltage change best to the operations of the devices in the LSI.